Such a relay should be not only of compact construction but also stable against shocks occurring, for example, upon a sudden stop or acceleration of the vehicle. Since most of these shocks act essentially in a horizontal direction, it is customary to provide such relays with a generally horizontal armature which is vertically movable by the applied magnetic force to close or to open an electrical circuit. The armature is usually a plate hinged at one end to the associated electromagnetic yoke and provided at the opposite end with a movable contact confronting an associated stationary contact coacting therewith; the yoke is supported on a base traversed by leads such as pins or prongs serving to connect the exciting coil or coils of the yoke as well as the relay contacts in an electric circuit including a battery or other power supply. A spring or the like biases the armature away from the yoke to hold the contacts open (or, possibly, closed) in the unexcited state of the relay.
In the presence of strong vertical shocks, however, the armature of such a relay may be accidentally moved into its alternate position with resulting untimely closure or opening of the controlled circuit. Moreover, since the armature and its biasing spring or equivalent elastic means form a resonant system, vibrations of a frequency near the natural frequency of that system may result in a chattering of the contacts in the unexcited state of the relay. An increase in the biasing force to prevent such untimely operation requires, of course, a larger operating current for the energization of the relay coil.